1 <sect1 id="appendix.porting.abi" xreflabel="abi">
2 <?dbhtml filename="abi.html"?>
27 <title>ABI Policy and Guidelines</title>
32 <sect2 id="abi.cxx_interface">
33 <title>The C++ Interface</title>
36 C++ applications often dependent on specific language support
37 routines, say for throwing exceptions, or catching exceptions, and
38 perhaps also dependent on features in the C++ Standard Library.
42 The C++ Standard Library has many include files, types defined in
43 those include files, specific named functions, and other
44 behavior. The text of these behaviors, as written in source include
45 files, is called the Application Programing Interface, or API.
49 Furthermore, C++ source that is compiled into object files is
50 transformed by the compiler: it arranges objects with specific
51 alignment and in a particular layout, mangling names according to a
52 well-defined algorithm, has specific arrangements for the support of
53 virtual functions, etc. These details are defined as the compiler
54 Application Binary Interface, or ABI. The GNU C++ compiler uses an
55 industry-standard C++ ABI starting with version 3. Details can be
57 url="http://www.codesourcery.com/cxx-abi/abi.html"> ABI
58 specification</ulink>.
62 The GNU C++ compiler, g++, has a compiler command line option to
63 switch between various different C++ ABIs. This explicit version
64 switch is the flag <code>-fabi-version</code>. In addition, some
65 g++ command line options may change the ABI as a side-effect of
66 use. Such flags include <code>-fpack-struct</code> and
67 <code>-fno-exceptions</code>, but include others: see the complete
68 list in the GCC manual under the heading <ulink url="http://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#Code%20Gen%20Options">Options
69 for Code Generation Conventions</ulink>.
73 The configure options used when building a specific libstdc++
74 version may also impact the resulting library ABI. The available
75 configure options, and their impact on the library ABI, are
77 <link linkend="manual.intro.setup.configure">here</link>.
80 <para> Putting all of these ideas together results in the C++ Standard
81 library ABI, which is the compilation of a given library API by a
82 given compiler ABI. In a nutshell:
87 library API + compiler ABI = library ABI
92 The library ABI is mostly of interest for end-users who have
93 unresolved symbols and are linking dynamically to the C++ Standard
94 library, and who thus must be careful to compile their application
95 with a compiler that is compatible with the available C++ Standard
96 library binary. In this case, compatible is defined with the equation
97 above: given an application compiled with a given compiler ABI and
98 library API, it will work correctly with a Standard C++ Library
99 created with the same constraints.
103 To use a specific version of the C++ ABI, one must use a
104 corresponding GNU C++ toolchain (i.e., g++ and libstdc++) that
105 implements the C++ ABI in question.
110 <sect2 id="abi.versioning">
111 <title>Versioning</title>
113 <para> The C++ interface has evolved throughout the history of the GNU
114 C++ toolchain. With each release, various details have been changed so
115 as to give distinct versions to the C++ interface.
118 <sect3 id="abi.versioning.goals">
121 <para>Extending existing, stable ABIs. Versioning gives subsequent
122 releases of library binaries the ability to add new symbols and add
123 functionality, all the while retaining compatibility with the previous
124 releases in the series. Thus, program binaries linked with the initial
125 release of a library binary will still link correctly if the library
126 binary is replaced by carefully-managed subsequent library
127 binaries. This is called forward compatibility.
130 The reverse (backwards compatibility) is not true. It is not possible
131 to take program binaries linked with the latest version of a library
132 binary in a release series (with additional symbols added), substitute
133 in the initial release of the library binary, and remain link
137 <para>Allows multiple, incompatible ABIs to coexist at the same time.
141 <sect3 id="abi.versioning.history">
142 <title>History</title>
145 How can this complexity be managed? What does C++ versioning mean?
146 Because library and compiler changes often make binaries compiled
147 with one version of the GNU tools incompatible with binaries
148 compiled with other (either newer or older) versions of the same GNU
149 tools, specific techniques are used to make managing this complexity
154 The following techniques are used:
159 <listitem><para>Release versioning on the libgcc_s.so binary. </para>
161 <para>This is implemented via file names and the ELF
162 <constant>DT_SONAME</constant> mechanism (at least on ELF
163 systems). It is versioned as follows:
167 <listitem><para>gcc-3.0.0: libgcc_s.so.1</para></listitem>
168 <listitem><para>gcc-3.0.1: libgcc_s.so.1</para></listitem>
169 <listitem><para>gcc-3.0.2: libgcc_s.so.1</para></listitem>
170 <listitem><para>gcc-3.0.3: libgcc_s.so.1</para></listitem>
171 <listitem><para>gcc-3.0.4: libgcc_s.so.1</para></listitem>
172 <listitem><para>gcc-3.1.0: libgcc_s.so.1</para></listitem>
173 <listitem><para>gcc-3.1.1: libgcc_s.so.1</para></listitem>
174 <listitem><para>gcc-3.2.0: libgcc_s.so.1</para></listitem>
175 <listitem><para>gcc-3.2.1: libgcc_s.so.1</para></listitem>
176 <listitem><para>gcc-3.2.2: libgcc_s.so.1</para></listitem>
177 <listitem><para>gcc-3.2.3: libgcc_s.so.1</para></listitem>
178 <listitem><para>gcc-3.3.0: libgcc_s.so.1</para></listitem>
179 <listitem><para>gcc-3.3.1: libgcc_s.so.1</para></listitem>
180 <listitem><para>gcc-3.3.2: libgcc_s.so.1</para></listitem>
181 <listitem><para>gcc-3.3.3: libgcc_s.so.1</para></listitem>
182 <listitem><para>gcc-3.4.x, gcc-4.[0-5].x: libgcc_s.so.1</para></listitem>
185 <para>For m68k-linux the versions differ as follows: </para>
188 <listitem><para>gcc-3.4.x, gcc-4.[0-5].x: libgcc_s.so.1
189 when configuring <code>--with-sjlj-exceptions</code>, or
190 libgcc_s.so.2 </para> </listitem>
193 <para>For hppa-linux the versions differ as follows: </para>
196 <listitem><para>gcc-3.4.x, gcc-4.[0-1].x: either libgcc_s.so.1
197 when configuring <code>--with-sjlj-exceptions</code>, or
198 libgcc_s.so.2 </para> </listitem>
199 <listitem><para>gcc-4.[2-5].x: either libgcc_s.so.3 when configuring
200 <code>--with-sjlj-exceptions</code>) or libgcc_s.so.4
206 <listitem><para>Symbol versioning on the libgcc_s.so binary.</para>
208 <para>It is versioned with the following labels and version
209 definitions, where the version definition is the maximum for a
210 particular release. Labels are cumulative. If a particular release
211 is not listed, it has the same version labels as the preceding
214 <para>This corresponds to the mapfile: gcc/libgcc-std.ver</para>
216 <listitem><para>gcc-3.0.0: GCC_3.0</para></listitem>
217 <listitem><para>gcc-3.3.0: GCC_3.3</para></listitem>
218 <listitem><para>gcc-3.3.1: GCC_3.3.1</para></listitem>
219 <listitem><para>gcc-3.3.2: GCC_3.3.2</para></listitem>
220 <listitem><para>gcc-3.3.4: GCC_3.3.4</para></listitem>
221 <listitem><para>gcc-3.4.0: GCC_3.4</para></listitem>
222 <listitem><para>gcc-3.4.2: GCC_3.4.2</para></listitem>
223 <listitem><para>gcc-3.4.4: GCC_3.4.4</para></listitem>
224 <listitem><para>gcc-4.0.0: GCC_4.0.0</para></listitem>
225 <listitem><para>gcc-4.1.0: GCC_4.1.0</para></listitem>
226 <listitem><para>gcc-4.2.0: GCC_4.2.0</para></listitem>
227 <listitem><para>gcc-4.3.0: GCC_4.3.0</para></listitem>
228 <listitem><para>gcc-4.4.0: GCC_4.4.0</para></listitem>
234 Release versioning on the libstdc++.so binary, implemented in
235 the same was as the libgcc_s.so binary above. Listed is the
236 filename: <constant>DT_SONAME</constant> can be deduced from
237 the filename by removing the last two period-delimited numbers. For
238 example, filename <filename>libstdc++.so.5.0.4</filename>
239 corresponds to a <constant>DT_SONAME</constant> of
240 <constant>libstdc++.so.5</constant>. Binaries with equivalent
241 <constant>DT_SONAME</constant>s are forward-compatibile: in
242 the table below, releases incompatible with the previous
243 one are explicitly noted.
246 <para>It is versioned as follows:
249 <listitem><para>gcc-3.0.0: libstdc++.so.3.0.0</para></listitem>
250 <listitem><para>gcc-3.0.1: libstdc++.so.3.0.1</para></listitem>
251 <listitem><para>gcc-3.0.2: libstdc++.so.3.0.2</para></listitem>
252 <listitem><para>gcc-3.0.3: libstdc++.so.3.0.2 (See Note 1)</para></listitem>
253 <listitem><para>gcc-3.0.4: libstdc++.so.3.0.4</para></listitem>
254 <listitem><para>gcc-3.1.0: libstdc++.so.4.0.0 <emphasis>(Incompatible with previous)</emphasis></para></listitem>
255 <listitem><para>gcc-3.1.1: libstdc++.so.4.0.1</para></listitem>
256 <listitem><para>gcc-3.2.0: libstdc++.so.5.0.0 <emphasis>(Incompatible with previous)</emphasis></para></listitem>
257 <listitem><para>gcc-3.2.1: libstdc++.so.5.0.1</para></listitem>
258 <listitem><para>gcc-3.2.2: libstdc++.so.5.0.2</para></listitem>
259 <listitem><para>gcc-3.2.3: libstdc++.so.5.0.3 (See Note 2)</para></listitem>
260 <listitem><para>gcc-3.3.0: libstdc++.so.5.0.4</para></listitem>
261 <listitem><para>gcc-3.3.1: libstdc++.so.5.0.5</para></listitem>
262 <listitem><para>gcc-3.3.2: libstdc++.so.5.0.5</para></listitem>
263 <listitem><para>gcc-3.3.3: libstdc++.so.5.0.5</para></listitem>
264 <listitem><para>gcc-3.4.0: libstdc++.so.6.0.0 <emphasis>(Incompatible with previous)</emphasis></para></listitem>
265 <listitem><para>gcc-3.4.1: libstdc++.so.6.0.1</para></listitem>
266 <listitem><para>gcc-3.4.2: libstdc++.so.6.0.2</para></listitem>
267 <listitem><para>gcc-3.4.3: libstdc++.so.6.0.3</para></listitem>
268 <listitem><para>gcc-3.4.4: libstdc++.so.6.0.3</para></listitem>
269 <listitem><para>gcc-3.4.5: libstdc++.so.6.0.3</para></listitem>
270 <listitem><para>gcc-3.4.6: libstdc++.so.6.0.3</para></listitem>
271 <listitem><para>gcc-4.0.0: libstdc++.so.6.0.4</para></listitem>
272 <listitem><para>gcc-4.0.1: libstdc++.so.6.0.5</para></listitem>
273 <listitem><para>gcc-4.0.2: libstdc++.so.6.0.6</para></listitem>
274 <listitem><para>gcc-4.0.3: libstdc++.so.6.0.7</para></listitem>
275 <listitem><para>gcc-4.1.0: libstdc++.so.6.0.7</para></listitem>
276 <listitem><para>gcc-4.1.1: libstdc++.so.6.0.8</para></listitem>
277 <listitem><para>gcc-4.1.2: libstdc++.so.6.0.8</para></listitem>
278 <listitem><para>gcc-4.2.0: libstdc++.so.6.0.9</para></listitem>
279 <listitem><para>gcc-4.2.1: libstdc++.so.6.0.9 (See Note 3)</para></listitem>
280 <listitem><para>gcc-4.2.2: libstdc++.so.6.0.9</para></listitem>
281 <listitem><para>gcc-4.2.3: libstdc++.so.6.0.9</para></listitem>
282 <listitem><para>gcc-4.2.4: libstdc++.so.6.0.9</para></listitem>
283 <listitem><para>gcc-4.3.0: libstdc++.so.6.0.10</para></listitem>
284 <listitem><para>gcc-4.3.1: libstdc++.so.6.0.10</para></listitem>
285 <listitem><para>gcc-4.3.2: libstdc++.so.6.0.10</para></listitem>
286 <listitem><para>gcc-4.3.3: libstdc++.so.6.0.10</para></listitem>
287 <listitem><para>gcc-4.3.4: libstdc++.so.6.0.10</para></listitem>
288 <listitem><para>gcc-4.4.0: libstdc++.so.6.0.11</para></listitem>
289 <listitem><para>gcc-4.4.1: libstdc++.so.6.0.12</para></listitem>
290 <listitem><para>gcc-4.4.2: libstdc++.so.6.0.13</para></listitem>
291 <listitem><para>gcc-4.5.0: libstdc++.so.6.0.14</para></listitem>
294 Note 1: Error should be libstdc++.so.3.0.3.
297 Note 2: Not strictly required.
300 Note 3: This release (but not previous or subsequent) has one
301 known incompatibility, see <ulink
302 url="http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33678">33678</ulink>
303 in the GCC bug database.
307 <listitem><para>Symbol versioning on the libstdc++.so binary.</para>
309 <para>mapfile: libstdc++/config/linker-map.gnu</para>
310 <para>It is versioned with the following labels and version
311 definitions, where the version definition is the maximum for a
312 particular release. Note, only symbol which are newly introduced
313 will use the maximum version definition. Thus, for release series
314 with the same label, but incremented version definitions, the later
315 release has both versions. (An example of this would be the
316 gcc-3.2.1 release, which has GLIBCPP_3.2.1 for new symbols and
317 GLIBCPP_3.2 for symbols that were introduced in the gcc-3.2.0
318 release.) If a particular release is not listed, it has the same
319 version labels as the preceding release.
322 <listitem><para>gcc-3.0.0: (Error, not versioned)</para></listitem>
323 <listitem><para>gcc-3.0.1: (Error, not versioned)</para></listitem>
324 <listitem><para>gcc-3.0.2: (Error, not versioned)</para></listitem>
325 <listitem><para>gcc-3.0.3: (Error, not versioned)</para></listitem>
326 <listitem><para>gcc-3.0.4: (Error, not versioned)</para></listitem>
327 <listitem><para>gcc-3.1.0: GLIBCPP_3.1, CXXABI_1</para></listitem>
328 <listitem><para>gcc-3.1.1: GLIBCPP_3.1, CXXABI_1</para></listitem>
329 <listitem><para>gcc-3.2.0: GLIBCPP_3.2, CXXABI_1.2</para></listitem>
330 <listitem><para>gcc-3.2.1: GLIBCPP_3.2.1, CXXABI_1.2</para></listitem>
331 <listitem><para>gcc-3.2.2: GLIBCPP_3.2.2, CXXABI_1.2</para></listitem>
332 <listitem><para>gcc-3.2.3: GLIBCPP_3.2.2, CXXABI_1.2</para></listitem>
333 <listitem><para>gcc-3.3.0: GLIBCPP_3.2.2, CXXABI_1.2.1</para></listitem>
334 <listitem><para>gcc-3.3.1: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem>
335 <listitem><para>gcc-3.3.2: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem>
336 <listitem><para>gcc-3.3.3: GLIBCPP_3.2.3, CXXABI_1.2.1</para></listitem>
337 <listitem><para>gcc-3.4.0: GLIBCXX_3.4, CXXABI_1.3</para></listitem>
338 <listitem><para>gcc-3.4.1: GLIBCXX_3.4.1, CXXABI_1.3</para></listitem>
339 <listitem><para>gcc-3.4.2: GLIBCXX_3.4.2</para></listitem>
340 <listitem><para>gcc-3.4.3: GLIBCXX_3.4.3</para></listitem>
341 <listitem><para>gcc-4.0.0: GLIBCXX_3.4.4, CXXABI_1.3.1</para></listitem>
342 <listitem><para>gcc-4.0.1: GLIBCXX_3.4.5</para></listitem>
343 <listitem><para>gcc-4.0.2: GLIBCXX_3.4.6</para></listitem>
344 <listitem><para>gcc-4.0.3: GLIBCXX_3.4.7</para></listitem>
345 <listitem><para>gcc-4.1.1: GLIBCXX_3.4.8</para></listitem>
346 <listitem><para>gcc-4.2.0: GLIBCXX_3.4.9</para></listitem>
347 <listitem><para>gcc-4.3.0: GLIBCXX_3.4.10, CXXABI_1.3.2</para></listitem>
348 <listitem><para>gcc-4.4.0: GLIBCXX_3.4.11, CXXABI_1.3.3</para></listitem>
349 <listitem><para>gcc-4.4.1: GLIBCXX_3.4.12, CXXABI_1.3.3</para></listitem>
350 <listitem><para>gcc-4.4.2: GLIBCXX_3.4.13, CXXABI_1.3.3</para></listitem>
351 <listitem><para>gcc-4.5.0: GLIBCXX_3.4.14, CXXABI_1.3.4</para></listitem>
356 <para>Incremental bumping of a compiler pre-defined macro,
357 __GXX_ABI_VERSION. This macro is defined as the version of the
358 compiler v3 ABI, with g++ 3.0.x being version 100. This macro will
359 be automatically defined whenever g++ is used (the curious can
360 test this by invoking g++ with the '-v' flag.)
364 This macro was defined in the file "lang-specs.h" in the gcc/cp directory.
365 Later versions defined it in "c-common.c" in the gcc directory, and from
366 G++ 3.4 it is defined in c-cppbuiltin.c and its value determined by the
367 '-fabi-version' command line option.
371 It is versioned as follows, where 'n' is given by '-fabi-version=n':
374 <listitem><para>gcc-3.0.x: 100</para></listitem>
375 <listitem><para>gcc-3.1.x: 100 (Error, should be 101)</para></listitem>
376 <listitem><para>gcc-3.2.x: 102</para></listitem>
377 <listitem><para>gcc-3.3.x: 102</para></listitem>
378 <listitem><para>gcc-3.4.x, gcc-4.[0-5].x: 102 (when n=1)</para></listitem>
379 <listitem><para>gcc-3.4.x, gcc-4.[0-5].x: 1000 + n (when n>1) </para></listitem>
380 <listitem><para>gcc-3.4.x, gcc-4.[0-5].x: 999999 (when n=0)</para></listitem>
386 <para>Changes to the default compiler option for
387 <code>-fabi-version</code>.
390 It is versioned as follows:
393 <listitem><para>gcc-3.0.x: (Error, not versioned) </para></listitem>
394 <listitem><para>gcc-3.1.x: (Error, not versioned) </para></listitem>
395 <listitem><para>gcc-3.2.x: <code>-fabi-version=1</code></para></listitem>
396 <listitem><para>gcc-3.3.x: <code>-fabi-version=1</code></para></listitem>
397 <listitem><para>gcc-3.4.x, gcc-4.[0-5].x: <code>-fabi-version=2</code> <emphasis>(Incompatible with previous)</emphasis></para></listitem>
403 <para>Incremental bumping of a library pre-defined macro. For releases
404 before 3.4.0, the macro is __GLIBCPP__. For later releases, it's
405 __GLIBCXX__. (The libstdc++ project generously changed from CPP to
406 CXX throughout its source to allow the "C" pre-processor the CPP
407 macro namespace.) These macros are defined as the date the library
408 was released, in compressed ISO date format, as an unsigned long.
412 This macro is defined in the file "c++config" in the
413 "libstdc++/include/bits" directory. (Up to gcc-4.1.0, it was
414 changed every night by an automated script. Since gcc-4.1.0, it is
415 the same value as gcc/DATESTAMP.)
418 It is versioned as follows:
421 <listitem><para>gcc-3.0.0: 20010615</para></listitem>
422 <listitem><para>gcc-3.0.1: 20010819</para></listitem>
423 <listitem><para>gcc-3.0.2: 20011023</para></listitem>
424 <listitem><para>gcc-3.0.3: 20011220</para></listitem>
425 <listitem><para>gcc-3.0.4: 20020220</para></listitem>
426 <listitem><para>gcc-3.1.0: 20020514</para></listitem>
427 <listitem><para>gcc-3.1.1: 20020725</para></listitem>
428 <listitem><para>gcc-3.2.0: 20020814</para></listitem>
429 <listitem><para>gcc-3.2.1: 20021119</para></listitem>
430 <listitem><para>gcc-3.2.2: 20030205</para></listitem>
431 <listitem><para>gcc-3.2.3: 20030422</para></listitem>
432 <listitem><para>gcc-3.3.0: 20030513</para></listitem>
433 <listitem><para>gcc-3.3.1: 20030804</para></listitem>
434 <listitem><para>gcc-3.3.2: 20031016</para></listitem>
435 <listitem><para>gcc-3.3.3: 20040214</para></listitem>
436 <listitem><para>gcc-3.4.0: 20040419</para></listitem>
437 <listitem><para>gcc-3.4.1: 20040701</para></listitem>
438 <listitem><para>gcc-3.4.2: 20040906</para></listitem>
439 <listitem><para>gcc-3.4.3: 20041105</para></listitem>
440 <listitem><para>gcc-3.4.4: 20050519</para></listitem>
441 <listitem><para>gcc-3.4.5: 20051201</para></listitem>
442 <listitem><para>gcc-3.4.6: 20060306</para></listitem>
443 <listitem><para>gcc-4.0.0: 20050421</para></listitem>
444 <listitem><para>gcc-4.0.1: 20050707</para></listitem>
445 <listitem><para>gcc-4.0.2: 20050921</para></listitem>
446 <listitem><para>gcc-4.0.3: 20060309</para></listitem>
447 <listitem><para>gcc-4.1.0: 20060228</para></listitem>
448 <listitem><para>gcc-4.1.1: 20060524</para></listitem>
449 <listitem><para>gcc-4.1.2: 20070214</para></listitem>
450 <listitem><para>gcc-4.2.0: 20070514</para></listitem>
451 <listitem><para>gcc-4.2.1: 20070719</para></listitem>
452 <listitem><para>gcc-4.2.2: 20071007</para></listitem>
453 <listitem><para>gcc-4.2.3: 20080201</para></listitem>
454 <listitem><para>gcc-4.2.4: 20080519</para></listitem>
455 <listitem><para>gcc-4.3.0: 20080306</para></listitem>
456 <listitem><para>gcc-4.3.1: 20080606</para></listitem>
457 <listitem><para>gcc-4.3.2: 20080827</para></listitem>
458 <listitem><para>gcc-4.3.3: 20090124</para></listitem>
459 <listitem><para>gcc-4.4.0: 20090421</para></listitem>
460 <listitem><para>gcc-4.4.1: 20090722</para></listitem>
461 <listitem><para>gcc-4.4.2: 20091015</para></listitem>
468 Incremental bumping of a library pre-defined macro,
469 _GLIBCPP_VERSION. This macro is defined as the released version of
470 the library, as a string literal. This is only implemented in
471 gcc-3.1.0 releases and higher, and is deprecated in 3.4 (where it
472 is called _GLIBCXX_VERSION).
476 This macro is defined in the file "c++config" in the
477 "libstdc++/include/bits" directory and is generated
478 automatically by autoconf as part of the configure-time generation
483 It is versioned as follows:
486 <listitem><para>gcc-3.0.0: "3.0.0"</para></listitem>
487 <listitem><para>gcc-3.0.1: "3.0.0" (Error, should be "3.0.1")</para></listitem>
488 <listitem><para>gcc-3.0.2: "3.0.0" (Error, should be "3.0.2")</para></listitem>
489 <listitem><para>gcc-3.0.3: "3.0.0" (Error, should be "3.0.3")</para></listitem>
490 <listitem><para>gcc-3.0.4: "3.0.0" (Error, should be "3.0.4")</para></listitem>
491 <listitem><para>gcc-3.1.0: "3.1.0"</para></listitem>
492 <listitem><para>gcc-3.1.1: "3.1.1"</para></listitem>
493 <listitem><para>gcc-3.2.0: "3.2"</para></listitem>
494 <listitem><para>gcc-3.2.1: "3.2.1"</para></listitem>
495 <listitem><para>gcc-3.2.2: "3.2.2"</para></listitem>
496 <listitem><para>gcc-3.2.3: "3.2.3"</para></listitem>
497 <listitem><para>gcc-3.3.0: "3.3"</para></listitem>
498 <listitem><para>gcc-3.3.1: "3.3.1"</para></listitem>
499 <listitem><para>gcc-3.3.2: "3.3.2"</para></listitem>
500 <listitem><para>gcc-3.3.3: "3.3.3"</para></listitem>
501 <listitem><para>gcc-3.4.x: "version-unused"</para></listitem>
502 <listitem><para>gcc-4.[0-5].x: "version-unused"</para></listitem>
509 Matching each specific C++ compiler release to a specific set of
510 C++ include files. This is only implemented in gcc-3.1.1 releases
514 All C++ includes are installed in include/c++, then nest in a
515 directory hierarchy corresponding to the C++ compiler's released
516 version. This version corresponds to the variable "gcc_version" in
517 "libstdc++/acinclude.m4," and more details can be found in that
518 file's macro GLIBCXX_CONFIGURE (GLIBCPP_CONFIGURE before gcc-3.4.0).
521 C++ includes are versioned as follows:
524 <listitem><para>gcc-3.0.0: include/g++-v3</para></listitem>
525 <listitem><para>gcc-3.0.1: include/g++-v3</para></listitem>
526 <listitem><para>gcc-3.0.2: include/g++-v3</para></listitem>
527 <listitem><para>gcc-3.0.3: include/g++-v3</para></listitem>
528 <listitem><para>gcc-3.0.4: include/g++-v3</para></listitem>
529 <listitem><para>gcc-3.1.0: include/g++-v3</para></listitem>
530 <listitem><para>gcc-3.1.1: include/c++/3.1.1</para></listitem>
531 <listitem><para>gcc-3.2.0: include/c++/3.2</para></listitem>
532 <listitem><para>gcc-3.2.1: include/c++/3.2.1</para></listitem>
533 <listitem><para>gcc-3.2.2: include/c++/3.2.2</para></listitem>
534 <listitem><para>gcc-3.2.3: include/c++/3.2.3</para></listitem>
535 <listitem><para>gcc-3.3.0: include/c++/3.3</para></listitem>
536 <listitem><para>gcc-3.3.1: include/c++/3.3.1</para></listitem>
537 <listitem><para>gcc-3.3.2: include/c++/3.3.2</para></listitem>
538 <listitem><para>gcc-3.3.3: include/c++/3.3.3</para></listitem>
539 <listitem><para>gcc-3.4.0: include/c++/3.4.0</para></listitem>
540 <listitem><para>gcc-3.4.1: include/c++/3.4.1</para></listitem>
541 <listitem><para>gcc-3.4.2: include/c++/3.4.2</para></listitem>
542 <listitem><para>gcc-3.4.3: include/c++/3.4.3</para></listitem>
543 <listitem><para>gcc-3.4.4: include/c++/3.4.4</para></listitem>
544 <listitem><para>gcc-3.4.5: include/c++/3.4.5</para></listitem>
545 <listitem><para>gcc-3.4.6: include/c++/3.4.6</para></listitem>
546 <listitem><para>gcc-4.0.0: include/c++/4.0.0</para></listitem>
547 <listitem><para>gcc-4.0.1: include/c++/4.0.1</para></listitem>
548 <listitem><para>gcc-4.0.2: include/c++/4.0.2</para></listitem>
549 <listitem><para>gcc-4.0.3: include/c++/4.0.3</para></listitem>
550 <listitem><para>gcc-4.1.0: include/c++/4.1.0</para></listitem>
551 <listitem><para>gcc-4.1.1: include/c++/4.1.1</para></listitem>
552 <listitem><para>gcc-4.1.2: include/c++/4.1.2</para></listitem>
553 <listitem><para>gcc-4.2.0: include/c++/4.2.0</para></listitem>
554 <listitem><para>gcc-4.2.1: include/c++/4.2.1</para></listitem>
555 <listitem><para>gcc-4.2.2: include/c++/4.2.2</para></listitem>
556 <listitem><para>gcc-4.2.3: include/c++/4.2.3</para></listitem>
557 <listitem><para>gcc-4.2.4: include/c++/4.2.4</para></listitem>
558 <listitem><para>gcc-4.3.0: include/c++/4.3.0</para></listitem>
559 <listitem><para>gcc-4.3.1: include/c++/4.3.1</para></listitem>
560 <listitem><para>gcc-4.3.3: include/c++/4.3.3</para></listitem>
561 <listitem><para>gcc-4.3.4: include/c++/4.3.4</para></listitem>
562 <listitem><para>gcc-4.4.0: include/c++/4.4.0</para></listitem>
563 <listitem><para>gcc-4.4.1: include/c++/4.4.1</para></listitem>
564 <listitem><para>gcc-4.4.2: include/c++/4.4.2</para></listitem>
565 <listitem><para>gcc-4.5.0: include/c++/4.5.0</para></listitem>
572 Taken together, these techniques can accurately specify interface
573 and implementation changes in the GNU C++ tools themselves. Used
574 properly, they allow both the GNU C++ tools implementation, and
575 programs using them, an evolving yet controlled development that
576 maintains backward compatibility.
582 <sect3 id="abi.versioning.prereq">
583 <title>Prerequisites</title>
585 Minimum environment that supports a versioned ABI: A supported
586 dynamic linker, a GNU linker of sufficient vintage to understand
587 demangled C++ name globbing (ld), a shared executable compiled
588 with g++, and shared libraries (libgcc_s, libstdc++) compiled by
589 a compiler (g++) with a compatible ABI. Phew.
593 On top of all that, an additional constraint: libstdc++ did not
594 attempt to version symbols (or age gracefully, really) until
599 Most modern Linux and BSD versions, particularly ones using
600 gcc-3.1.x tools and more recent vintages, will meet the
605 <sect3 id="abi.versioning.config">
606 <title>Configuring</title>
609 It turns out that most of the configure options that change
610 default behavior will impact the mangled names of exported
611 symbols, and thus impact versioning and compatibility.
615 For more information on configure options, including ABI
617 http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html
621 There is one flag that explicitly deals with symbol versioning:
626 In particular, libstdc++/acinclude.m4 has a macro called
627 GLIBCXX_ENABLE_SYMVERS that defaults to yes (or the argument
628 passed in via --enable-symvers=foo). At that point, the macro
629 attempts to make sure that all the requirement for symbol
630 versioning are in place. For more information, please consult
635 <sect3 id="abi.versioning.active">
636 <title>Checking Active</title>
639 When the GNU C++ library is being built with symbol versioning
640 on, you should see the following at configure time for
646 checking versioning on shared library symbols... gnu
651 If you don't see this line in the configure output, or if this line
652 appears but the last word is 'no', then you are out of luck.
656 If the compiler is pre-installed, a quick way to test is to compile
657 the following (or any) simple C++ file and link it to the shared
662 #include <iostream>
665 { std::cout << "hello" << std::endl; return 0; }
667 %g++ hello.cc -o hello.out
670 libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x00764000)
671 libm.so.6 => /lib/tls/libm.so.6 (0x004a8000)
672 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x40016000)
673 libc.so.6 => /lib/tls/libc.so.6 (0x0036d000)
674 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
680 If you see symbols in the resulting output with "GLIBCXX_3" as part
681 of the name, then the executable is versioned. Here's an example:
685 <code>U _ZNSt8ios_base4InitC1Ev@@GLIBCXX_3.4</code>
691 <sect2 id="abi.changes_allowed">
692 <title>Allowed Changes</title>
695 The following will cause the library minor version number to
696 increase, say from "libstdc++.so.3.0.4" to "libstdc++.so.3.0.5".
699 <listitem><para>Adding an exported global or static data member</para></listitem>
700 <listitem><para>Adding an exported function, static or non-virtual member function</para></listitem>
701 <listitem><para>Adding an exported symbol or symbols by additional instantiations</para></listitem>
704 Other allowed changes are possible.
709 <sect2 id="abi.changes_no">
710 <title>Prohibited Changes</title>
713 The following non-exhaustive list will cause the library major version
714 number to increase, say from "libstdc++.so.3.0.4" to
715 "libstdc++.so.4.0.0".
719 <listitem><para>Changes in the gcc/g++ compiler ABI</para></listitem>
720 <listitem><para>Changing size of an exported symbol</para></listitem>
721 <listitem><para>Changing alignment of an exported symbol</para></listitem>
722 <listitem><para>Changing the layout of an exported symbol</para></listitem>
723 <listitem><para>Changing mangling on an exported symbol</para></listitem>
724 <listitem><para>Deleting an exported symbol</para></listitem>
725 <listitem><para>Changing the inheritance properties of a type by adding or removing
726 base classes</para></listitem>
728 Changing the size, alignment, or layout of types
729 specified in the C++ standard. These may not necessarily be
730 instantiated or otherwise exported in the library binary, and
731 include all the required locale facets, as well as things like
732 std::basic_streambuf, et al.
735 <listitem><para> Adding an explicit copy constructor or destructor to a
736 class that would otherwise have implicit versions. This will change
737 the way the compiler deals with this class in by-value return
738 statements or parameters: instead of being passing instances of this
739 class in registers, the compiler will be forced to use memory. See <ulink url="http://www.codesourcery.com/cxx-abi/abi.html#calls"> this part</ulink>
740 of the C++ ABI documentation for further details.
749 <sect2 id="abi.impl">
750 <title>Implementation</title>
755 Separation of interface and implementation
758 This is accomplished by two techniques that separate the API from
759 the ABI: forcing undefined references to link against a library
760 binary for definitions.
765 <term>Include files have declarations, source files have defines</term>
769 For non-templatized types, such as much of <code>class
770 locale</code>, the appropriate standard C++ include, say
771 <code>locale</code>, can contain full declarations, while
772 various source files (say <code> locale.cc, locale_init.cc,
773 localename.cc</code>) contain definitions.
779 <term>Extern template on required types</term>
783 For parts of the standard that have an explicit list of
784 required instantiations, the GNU extension syntax <code> extern
785 template </code> can be used to control where template
786 definitions reside. By marking required instantiations as
787 <code> extern template </code> in include files, and providing
788 explicit instantiations in the appropriate instantiation files,
789 non-inlined template functions can be versioned. This technique
790 is mostly used on parts of the standard that require <code>
791 char</code> and <code> wchar_t</code> instantiations, and
792 includes <code> basic_string</code>, the locale facets, and the
793 types in <code> iostreams</code>.
801 In addition, these techniques have the additional benefit that they
802 reduce binary size, which can increase runtime performance.
808 Namespaces linking symbol definitions to export mapfiles
811 All symbols in the shared library binary are processed by a
812 linker script at build time that either allows or disallows
813 external linkage. Because of this, some symbols, regardless of
814 normal C/C++ linkage, are not visible. Symbols that are internal
815 have several appealing characteristics: by not exporting the
816 symbols, there are no relocations when the shared library is
817 started and thus this makes for faster runtime loading
818 performance by the underlying dynamic loading mechanism. In
819 addition, they have the possibility of changing without impacting
823 <para>The following namespaces are transformed by the mapfile:</para>
828 <term><code>namespace std</code></term>
829 <listitem><para> Defaults to exporting all symbols in label
830 <code>GLIBCXX</code> that do not begin with an underscore, i.e.,
831 <code>__test_func</code> would not be exported by default. Select
832 exceptional symbols are allowed to be visible.</para></listitem>
836 <term><code>namespace __gnu_cxx</code></term>
837 <listitem><para> Defaults to not exporting any symbols in label
838 <code>GLIBCXX</code>, select items are allowed to be visible.</para></listitem>
842 <term><code>namespace __gnu_internal</code></term>
843 <listitem><para> Defaults to not exported, no items are allowed to be visible.</para></listitem>
847 <term><code>namespace __cxxabiv1</code>, aliased to <code> namespace abi</code></term>
848 <listitem><para> Defaults to not exporting any symbols in label
849 <code>CXXABI</code>, select items are allowed to be visible.</para></listitem>
857 <listitem><para>Freezing the API</para>
858 <para>Disallowed changes, as above, are not made on a stable release
859 branch. Enforcement tends to be less strict with GNU extensions that
860 standard includes.</para>
866 <sect2 id="abi.testing">
867 <title>Testing</title>
869 <sect3 id="abi.testing.single">
870 <title>Single ABI Testing</title>
873 Testing for GNU C++ ABI changes is composed of two distinct
874 areas: testing the C++ compiler (g++) for compiler changes, and
875 testing the C++ library (libstdc++) for library changes.
879 Testing the C++ compiler ABI can be done various ways.
883 One. Intel ABI checker.
888 The second is yet unreleased, but has been announced on the gcc
889 mailing list. It is yet unspecified if these tools will be freely
890 available, and able to be included in a GNU project. Please contact
891 Mark Mitchell (mark@codesourcery.com) for more details, and current
897 Involves using the vlad.consistency test framework. This has also been
898 discussed on the gcc mailing lists.
902 Testing the C++ library ABI can also be done various ways.
907 (Brendan Kehoe, Jeff Law suggestion to run 'make check-c++' two ways,
908 one with a new compiler and an old library, and the other with an old
909 compiler and a new library, and look for testsuite regressions)
913 Details on how to set this kind of test up can be found here:
914 http://gcc.gnu.org/ml/gcc/2002-08/msg00142.html
919 Use the 'make check-abi' rule in the libstdc++ Makefile.
923 This is a proactive check the library ABI. Currently, exported symbol
924 names that are either weak or defined are checked against a last known
925 good baseline. Currently, this baseline is keyed off of 3.4.0
926 binaries, as this was the last time the .so number was incremented. In
927 addition, all exported names are demangled, and the exported objects
928 are checked to make sure they are the same size as the same object in
931 Notice that each baseline is relative to a <emphasis>default</emphasis>
932 configured library and compiler: in particular, if options such as
933 --enable-clocale, or --with-cpu, in case of multilibs, are used at
934 configure time, the check may fail, either because of substantive
935 differences or because of limitations of the current checking
940 This dataset is insufficient, yet a start. Also needed is a
941 comprehensive check for all user-visible types part of the standard
942 library for sizeof() and alignof() changes.
946 Verifying compatible layouts of objects is not even attempted. It
947 should be possible to use sizeof, alignof, and offsetof to compute
948 offsets for each structure and type in the standard library, saving to
949 another datafile. Then, compute this in a similar way for new
950 binaries, and look for differences.
954 Another approach might be to use the -fdump-class-hierarchy flag to
955 get information. However, currently this approach gives insufficient
956 data for use in library testing, as class data members, their offsets,
957 and other detailed data is not displayed with this flag.
958 (See g++/7470 on how this was used to find bugs.)
962 Perhaps there are other C++ ABI checkers. If so, please notify
963 us. We'd like to know about them!
967 <sect3 id="abi.testing.multi">
968 <title>Multiple ABI Testing</title>
970 A "C" application, dynamically linked to two shared libraries, liba,
971 libb. The dependent library liba is C++ shared library compiled with
972 gcc-3.3.x, and uses io, exceptions, locale, etc. The dependent library
973 libb is a C++ shared library compiled with gcc-3.4.x, and also uses io,
974 exceptions, locale, etc.
977 <para> As above, libone is constructed as follows: </para>
979 %$bld/H-x86-gcc-3.4.0/bin/g++ -fPIC -DPIC -c a.cc
981 %$bld/H-x86-gcc-3.4.0/bin/g++ -shared -Wl,-soname -Wl,libone.so.1 -Wl,-O1 -Wl,-z,defs a.o -o libone.so.1.0.0
983 %ln -s libone.so.1.0.0 libone.so
985 %$bld/H-x86-gcc-3.4.0/bin/g++ -c a.cc
990 <para> And, libtwo is constructed as follows: </para>
993 %$bld/H-x86-gcc-3.3.3/bin/g++ -fPIC -DPIC -c b.cc
995 %$bld/H-x86-gcc-3.3.3/bin/g++ -shared -Wl,-soname -Wl,libtwo.so.1 -Wl,-O1 -Wl,-z,defs b.o -o libtwo.so.1.0.0
997 %ln -s libtwo.so.1.0.0 libtwo.so
999 %$bld/H-x86-gcc-3.3.3/bin/g++ -c b.cc
1001 %ar cru libtwo.a b.o
1004 <para> ...with the resulting libraries looking like </para>
1008 %ldd libone.so.1.0.0
1009 libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x40016000)
1010 libm.so.6 => /lib/tls/libm.so.6 (0x400fa000)
1011 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x4011c000)
1012 libc.so.6 => /lib/tls/libc.so.6 (0x40125000)
1013 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
1015 %ldd libtwo.so.1.0.0
1016 libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x40027000)
1017 libm.so.6 => /lib/tls/libm.so.6 (0x400e1000)
1018 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x40103000)
1019 libc.so.6 => /lib/tls/libc.so.6 (0x4010c000)
1020 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
1025 Then, the "C" compiler is used to compile a source file that uses
1026 functions from each library.
1029 gcc test.c -g -O2 -L. -lone -ltwo /usr/lib/libstdc++.so.5 /usr/lib/libstdc++.so.6
1033 Which gives the expected:
1039 libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x00764000)
1040 libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x40015000)
1041 libc.so.6 => /lib/tls/libc.so.6 (0x0036d000)
1042 libm.so.6 => /lib/tls/libm.so.6 (0x004a8000)
1043 libgcc_s.so.1 => /mnt/hd/bld/gcc/gcc/libgcc_s.so.1 (0x400e5000)
1044 /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00355000)
1049 This resulting binary, when executed, will be able to safely use
1050 code from both liba, and the dependent libstdc++.so.6, and libb,
1051 with the dependent libstdc++.so.5.
1056 <sect2 id="abi.issues">
1057 <title>Outstanding Issues</title>
1060 Some features in the C++ language make versioning especially
1061 difficult. In particular, compiler generated constructs such as
1062 implicit instantiations for templates, typeinfo information, and
1063 virtual tables all may cause ABI leakage across shared library
1064 boundaries. Because of this, mixing C++ ABIs is not recommended at
1069 For more background on this issue, see these bugzilla entries:
1073 <ulink url="http://gcc.gnu.org/PR24660">24660: versioning weak symbols in libstdc++</ulink>
1077 <ulink url="http://gcc.gnu.org/PR19664">19664: libstdc++ headers should have pop/push of the visibility around the declarations</ulink>
1082 <bibliography id="abi.biblio">
1083 <title>Bibliography</title>
1086 <biblioid class="uri">
1087 <ulink url="http://abicheck.sourceforge.net/">
1089 ABIcheck, a vague idea of checking ABI compatibility
1096 <biblioid class="uri">
1097 <ulink url="http://www.codesourcery.com/public/cxx-abi/">
1106 <biblioid class="uri">
1107 <ulink url="http://www.intel.com/cd/software/products/asmo-na/eng/284736.htm">
1109 Intel Compilers for Linux Compatibility with the GNU Compilers
1116 <biblioid class="uri">
1117 <ulink url="http://docs.sun.com/app/docs/doc/817-1984">
1119 Sun Solaris 2.9 : Linker and Libraries Guide (document 816-1386)
1127 <biblioid class="uri">
1128 <ulink url="http://docs.sun.com/app/docs/doc/819-5266">
1130 Sun Solaris 2.9 : C++ Migration Guide (document 816-2459)
1137 <biblioid class="uri">
1138 <ulink url="http://people.redhat.com/drepper/dsohowto.pdf">
1140 How to Write Shared Libraries
1146 <firstname>Ulrich</firstname>
1147 <surname>Drepper</surname>
1152 <biblioid class="uri">
1153 <ulink url="http://www.arm.com/miscPDFs/8033.pdf">
1155 C++ ABI for the ARM Architecture
1162 <biblioid class="uri">
1163 <ulink url="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1976.html">
1165 Dynamic Shared Objects: Survey and Issues
1173 <firstname>Benjamin</firstname>
1174 <surname>Kosnik</surname>
1179 <biblioid class="uri">
1180 <ulink url="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2013.html">
1182 Versioning With Namespaces
1190 <firstname>Benjamin</firstname>
1191 <surname>Kosnik</surname>
1196 <biblioid class="uri">
1197 <ulink url="http://syrcose.ispras.ru/2009/files/SYRCoSE2009-CfP.pdf">
1199 Binary Compatibility of Shared Libraries Implemented in C++
1200 on GNU/Linux Systems
1208 <firstname>Pavel</firstname>
1209 <surname>Shved</surname>
1212 <firstname>Denis</firstname>
1213 <surname>Silakov</surname>